A multi slope output impedance controller is configured to vary the effective impedance Zeff_n of a power converter to reduce a current imbalance between power supplies in a masterless configuration of N parallel-connected power supplies while maintaining load regulation during start-up and steady-state operation. Generally speaking, the controller commands a high value of Zeff_n when iout_n is low to facilitate current sharing and reduce current imbalance ib between the power supplies and commands a low value of Zeff_n when iout_n is high to improve load regulation.
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14. A regulated power supply configured to supply power to a common load connected at a load terminal, said power supply comprising:
N parallel-connected power supplies in a masterless configuration configured to supply power to the load terminal where N is an integer of one or more, each said power supply comprising,
a power converter responsive to a command Vx_n to generate a controllable voltage vc_n across an effective output impedance Zeff_n to supply an output current iout_n at an output that is coupled through an external impedance zext_n to the load terminal;
a negative feedback controller is connected to provide a negative feedback loop in which a regulated voltage vreg_n at the output is compared to a setpoint voltage vsetpoint_n to control command Vx_n to regulate the regulated voltage vreg_n and an output voltage vout at the load terminal for varying load currents Iload; and
a multi slope output impedance controller configured to sense a current isense_n indicative of the output current iout_n to control the setpoint voltage vsetpoint_n to control the regulation of the regulated voltage vreg_n and the output voltage vout, said controller being responsive to a mode input to select either a single power supply or a multiple power supply configuration,
wherein in the multiple configuration of N>1, the controller is configured to reduce the setpoint voltage vsetpoint_n as the output current iout_n increases to facilitate load current sharing among the plurality of power supplies, command a high value of the effective output impedance Zeff_n for the output current iout_n less than a specified value to reduce a current imbalance ib between the power supplies and to command a low value of the effective output impedance Zeff_n for the output current iout_n greater than the specified value to improve regulation; and
wherein in the single configuration of N=1, the controller is configured to set a negative value for the effective output impedance Zeff_n to substantially offset a positive value of the external impedance zext_n to increase the setpoint voltage vsetpoint_n as the output current iout_n increases to improve load regulation.
1. A regulated power supply configured to supply power to a common load connected at a load terminal, said power supply comprising:
N parallel-connected power supplies in a masterless configuration configured to supply power to the load terminal where N is an integer of one or more, each said power supply comprising,
a power converter responsive to a command Vx_n to generate a controllable voltage vc_n across an effective output impedance Zeff_n to supply an output current iout_n at an output that is coupled through an external output impedance zext_n to the load terminal;
a negative feedback controller configured to provide a negative feedback loop in which a regulated voltage vreg_n at the output is compared to a setpoint voltage vsetpoint_n to control the command Vx_n to maintain regulation of the regulated voltage vreg_n and an output voltage vout at the load terminal for varying load currents IL; and
a multi slope output impedance controller responsive to a current isense_n indicative of the output current iout_n to control the setpoint voltage vsetpoint_n such that the regulated voltage vreg_n is reduced as the output current iout_n is increased to facilitate load current sharing among the plurality of power supplies, command a high value of the effective output impedance Zeff_n when the output current iout_n is less than a specified value to reduce a current imbalance ib between the power supplies and to command a low value of the effective output impedance Zeff_n when the output current iout_n is greater than the specified value to improve the regulation of the output voltage vout
wherein the multi slope output impedance controller is responsive to a mode input to select single or multiple power converter configurations,
wherein in the multiple configuration of N>1, the controller is configured to reduce the setpoint voltage vsetpoint_n as the output current iout_n increases to facilitate load current sharing among the plurality of power supplies and to command the high value of the Zeff_n for the iout_n less than the specified value to reduce the current imbalance ib and to command the low value of the Zeff_n for the iout_n greater than the specified value to improve load regulation;
wherein in the single configuration of N=1, the controller is configured to set a negative value for the Zeff_n to substantially offset a positive value of the zext_n to increase the setpoint voltage vsetpoint_n as the output current iout_n increases to improve load regulation.
2. The regulated power supply of
a coefficient generator controller (CGC) responsive to the current isense_n and a voltage reference Vref_n to generate a current reference, a gain command, a filter command and a setpoint command;
a current error amplifier that compares the current isense_n to the current reference to generate an error signal;
a programmable gain amplifier responsive to the gain command to command the high and low values of the effective output impedance Zeff_n and amplify the error signal;
a filter responsive to the filter command to filter the amplified error signal to limit a bandwidth of an output impedance control loop to be less than a bandwidth of the negative feedback loop that controls the regulated voltage Vreg; and
an amplifier responsive to the filtered amplified error signal and the setpoint command to generate the setpoint voltage vsetpoint_n such that when the current isense_n is greater than the current reference the setpoint voltage vsetpoint_n is reduced.
3. The regulated power supply of
4. The regulated power supply of
5. The regulated power supply of
6. The regulated power supply of
7. The regulated power supply of
8. The regulated power supply of
9. The regulated power supply of
10. The regulated power supply of
11. The regulated power supply of
12. The regulated power supply of
wherein during the start-up procedure, the controller is responsive to a start sync command to generate the command Vx_n to ramp the controllable voltage vc_n, hence the regulated voltage vreg_n up from zero volts to the setpoint voltage vsetpoint_n while commanding the effective output impedance Zeff_n to move from a start-up high value to reduce the current imbalance ib to a start-up low value to improve load regulation over a start-up period; and
wherein during the steady-state procedure, the controller is response to the command Vx_n to control regulation of the output voltage vout while commanding the effective output impedance Zeff_n to move between steady-state high and low values as the current Isense changes such that the effective output impedance Zeff_n decreases as the output current iout_n increases to reduce the current imbalance ib when the output current iout_n is low and to improve load regulation when the output current iout_n is high.
13. The regulated power supply of
wherein during the start-up procedure, the controller is responsive to a start sync command to generate the command Vx_n to ramp voltage vc_n, hence the regulated voltage vreg_n up from zero volts to the setpoint voltage vsetpoint_n while commanding the Zeff_n to move from a start-up high value to reduce the current imbalance ib to a start-up low value to improve load regulation over a start-up period; and
wherein during the steady-state procedure, the controller is response to the command Vx_n to control regulation of the vout while commanding the Zeff_n in response to the Isense to move between steady-state high and low values as the Isense changes such that the Zeff_n decreases as the iout_n increases to reduce current imbalance ib when the iout_n is low and to improve load regulation when the iout_n is high.
15. The regulated power supply of
wherein during the start-up procedure, the controller is responsive to a start sync command to generate the command Vx_n to ramp the controllable voltage vc_n, hence the regulated voltage vreg_n up from an initial value to the setpoint voltage vsetpoint_n while commanding the effective output impedance Zeff_n to move from a start-up high value to reduce the current imbalance ib to a start-up low value to improve load regulation over a start-up period; and
wherein during the steady-state procedure, the controller is response to the command Vx_n to control regulation of the output voltage vout while commanding the effective output impedance Zeff_n in response to the current Isense to move between a steady-state high and low values as the current isense_n changes such that the effective output impedance Zeff_n decreases as the output current Tout n increases to reduce the current imbalance ib when the output current iout_n is low and to improve load regulation when the output current iout_n is high.
16. The regulated power supply of
a coefficient generator controller (CGC) responsive to the current isense_n and a voltage reference Vref_n to generate a current reference, a gain command, a filter command and a setpoint command;
a current error amplifier that compares the current isense_n to the current reference to generate an error signal;
a programmable gain amplifier responsive to the gain command to command the high and low values of the effective output impedance Zeff_n and amplify the error signal;
a filter responsive to the filter command to filter the amplified error signal to limit a bandwidth of an output impedance control loop to be less than a bandwidth of the negative feedback loop that controls the regulated voltage Vreg; and
an amplifier responsive to the filtered amplified error signal and the setpoint command to generate the setpoint voltage vsetpoint_n such that when the current isense_n is greater than the current reference the setpoint voltage vsetpoint_n is reduced.
17. The regulated power supply of
18. The regulated power supply of
19. The regulated power supply of
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This application claims benefit of priority under 35 U.S.C. 119(e) to U.S. Provisional Application No. 63/289,884 entitled “Multi Slope Output Impedance Controller” and filed on Dec. 15, 2021, the entire contents of which are incorporated by reference.
This invention relates to regulated power supplies capable of supplying a range of load currents to a load and more particularly to a masterless configuration of N parallel-connected power supplies each of which includes a passively or synchronously rectified power converter connected in a negative feedback loop to facilitate sharing of the load current and maintain regulation of the output voltage.
A power supply may include a power converter that converts an unregulated DC input voltage Vin to a regulated DC output voltage Vout, usually at a different level, for supplying a range of load currents IL to a load. A vast variety of topologies for power converters have been introduced over the years. Further, the need for small size and high efficiency places additional limitations on the available topologies. Small size equates to high power density, and power density is the ratio of output power capability to converter volume.
A switching power converter (SPC) has an energy storage section and a switching control circuit such as a pulse width modulator (PWM), a primary switch, and a rectifier. The energy storage section is responsive to the selective application of the DC input voltage to produce a current and the regulated DC output voltage. The switching control circuit, primary switch and rectifier control the application of the DC input voltage to the energy storage section to set the value of the regulated DC output voltage.
Synchronous rectification has become a desirable alternative to passive rectifiers in power converters due to the increased power conversion efficiency that results at least in part from reduced power losses and higher density. While diodes only permit current flow in one direction, synchronous rectifiers such as MOSFETs, or other equivalent active switches permit current flow in either direction
Power supplies based on modular power converters are desirable as they allow sharing of power loads across multiple units and allow flexibility to scale the power solution for a variety of applications. As shown in
As shown in
To improve regulation, closed loop control with negative feedback is typically applied to the open loop power converter. A negative feedback controller 206 will force the output voltage Vreg_n of the power converter to be equal to a setpoint voltage V_setpoint_n, which is offset from the reference voltage Vref_n. An output impedance controller 208 is coupled to Vref_n and responsive to a sense current Isense_n, which is indicative of Iout_n, to generate an offset to form V_setpoint_n. A feature of negative feedback is to lower the open loop output impedance Zout_OL of the power converter by the loop gain of the negative feedback controller. If the negative feedback controller has an open loop gain of T then the closed loop output impedance of the power converter will be:
For example if T+1=60 dB then the open loop output impedance of the converter would be reduced by factor of 1000.
An output impedance controller 208 is coupled to Vref_n and responsive to a sense current Isense_n, which is indicative of Iout_n, to generate an offset to form V_setpoint_n. Controller 208 maintains a constant effective output impedance Zeff_n from ZoutCL for the power converter over the range of load currents. A typical controller 208 includes a current amplifier that compares Isense_n to a current reference (e.g. the midpoint of the load current range), a fixed gain amplifier to amplify the error signal, a filter that fixes a bandwidth of the output impedance control loop to be less than the bandwidth of the negative feedback loop that controls Vout and an amplifier produce the offset to generate V_setpoint_n. Typically, the bandwidth of the negative feedback loop drops as the load current is reduced. Therefore, the fixed bandwidth of the output impedance control loop must be set to be less than the bandwidth of the negative feedback loop for the lowest supported load current to avoid interaction between the control loops.
Ideally, all of the power converters 202 would have the exact same reference voltage, negative feedback loop etc. and would share the load current equally during start-up and steady-state over the entire supported range of load currents. However, in a masterless configuration each converter has its own Vref, which will vary within a specified tolerance, non-linearities, etc. This can lead to a current imbalance Ib among the power converters that leads to power inefficiency, stress on individual converters or a failure and shutdown of the power supply. In passively rectified power converters, at low load current IL and low Iout_n one power converter may dominate and supply 100% of the load current while the other power converters turn off. In synchronously rectified power converters, at low Iout_n a circulating current Ic will flow between the power converters. If Vc_1 does not exactly match Vc_2 due to differences in Vx1 and Vx2 or slight differences in α_1 and α_2 then a circulating current Ic will flow between the two converters:
where Zout_n=Zeff_n at this point. Once the output voltages of the power converters are well regulated and their output currents Iout_n>2*IC under a no load condition then Ic under load will be approximately zero.
As shown in
As shown in
During power converter startup, the output voltage of each converter is ramped from an initial value e.g., zero volts to the final setpoint voltage, by ramping the Vref_n. The “ramp” may be linear, a sequence of steps or a higher order function. When parallel converters are started in a masterless system, slight errors in the ramp rates of the converters and non-linear effects can create significant current imbalance Ib. For a masterless configuration of passively rectified power converters, the result will typically be that a single power converter will turn on and supply the load current as the output voltage is ramped up. Only when the load current, hence individual output currents Iout_n, are high enough will droop share be effective to turn on the other power converters and force sharing. As shown in
During steady-state, the power supply and the individual power converters will be required to source varying amounts of load current IL over a specified range while maintaining regulation of the output voltage Vout. For passively rectified converters, if the load current IL, hence the individual output currents Iout_n, are too small droop share can fail resulting in either one or a small number of the converters supplying the load current. In general, Iload has to exceed a certain value before all of the converters turn on and share the load current. As shown in
Known techniques pick a fixed value of Zeff that balances the competing requirements during start-up and steady-state to facilitate sharing, limit the current imbalance and maintain load regulation. A larger value of Zeff improves droop share to facilitate sharing at start-up or for low levels of load current and reduce current imbalance Ib while a smaller value of Zeff improves load regulation. The two must be compromised.
The following is a summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description and the defining claims that are presented later.
The present invention provides a multi slope output impedance controller capable of varying the effective impedance Zeff of a power converter to reduce a current imbalance between power supplies in a masterless configuration of N parallel-connected power supplies while maintaining load regulation or of setting a negative Zeff to optimize load regulation for a single power converter.
In an embodiment, a regulated power supply includes a plurality N of parallel-connected power supplies in a masterless configuration configured to supply power to a load terminal. Each power supply includes a power converter connected in a negative feedback loop with its own reference voltage Vref_n to supply an output current Iout_n through an external output impedance Zext_n (outside the negative feedback loop) to the load terminal. Acting independently the N power supplies together share the load current IL over a range of load currents and provide a regulated output voltage Vout over that range. The negative feedback loop is configurable to vary an effective output impedance Zeff_n of the power converter responsive to Iout_n to reduce the current imbalance Ib between the power supplies during start-up and steady-state while maintaining load regulation.
In an embodiment of the masterless configuration of N parallel-connected power supplies, each power converter is responsive to a command Vx_n to generate a controllable voltage Vc_n across Zeff_n to supply Iout_n at an output that is coupled through Zext_n to the load terminal. A negative feedback controller is configured to provide the negative feedback loop in which a regulated voltage Vreg_n at the output is compared to a setpoint voltage Vsetpoint_n (offset from Vref_n) to control command Vx_n to maintain regulation of Vreg_n and output voltage Vout at the load terminal for varying load currents IL. A multi slope output impedance controller is configured to sense a current Isense_n indicative of Iout_n to control Vsetpoint_n such that Vreg_n is reduced as Iout_n is increased to facilitate load current sharing among the plurality of power supplies (common droop share), command a high value of Zeff_n when Iout_n is less than a specified value to reduce a current imbalance Ib between the power supplies and to command a low value of Zeff_n when Iout_n is greater than the specified value to improve the regulation of Vout. The controller may command a low value of Zeff_n that is negative to partially offset Zext_n during steady-state to optimize regulation.
In an embodiment, the multi slope output impedance controller includes a coefficient generator controller (CGC) responsive to Isense_n, the switching frequency and voltage reference Vref_n to generate a current reference, a gain command, a filter command and a setpoint command. A current error amplifier compares Isense_n to the current reference to generate an error signal, a programmable gain amplifier responsive to the gain command commands the high and low values of Zeff_n amplifies the error signal, a filter responsive to the filter command filters the amplified error signal to limit a bandwidth of an output impedance control loop to be less than a bandwidth of the negative feedback loop that controls Vreg, and an amplifier responsive to the filtered amplified error signal and the setpoint command generates the setpoint voltage Vsetpoint_n such that when Isense_n is greater than the current reference the setpoint voltage Vsetpoint_n is reduced. The filter command is preferably generated such that the bandwidth of the output impedance control loop tracks the bandwidth of the negative feedback loop that controls Vreg up and down to better optimize performance over the range of supported load currents.
The power converters may be implemented as passively or synchronously rectified power converters. A passively rectified power converter is a single quadrant converter in which diodes may sink or source current but not both. At low levels of Iout_n, either during start-up or steady-state, this may manifest in one power converter supplying 100% of the load current with the other power converters turned off. Switching Zeff_n to a high value at low levels of Iout_n will force sharing of the load current among all of the power converters even at low levels of Iout_n and IL, preferably across the entire range of supported load currents. Switching Zeff_n to a low level when Iout_n is sufficiently large (and Vreg_n are sufficiently regulated), will improve the steady-state regulation. A synchronously rectified power converter is two quadrant converter in which active switches (synchronous rectifiers) may sink or source current. At low levels of Iout_n, either during start-up or steady-state, this may manifest in a circulating current Ic flowing among the power supplies. Switching Zeff_n to a high value at low levels of Iout_n will minimize Ic. Switching Zeff_n to a low level when Iout_n is sufficiently large (and Vreg_n are sufficiently regulated) that Ic is approximately zero (e.g., when Iout_n>2*Ic no load), will improve the steady-state regulation. In the case of passive rectification, the current imbalance Ib is the difference between how much of the load current each supply provides. In the case of synchronous rectification, the current imbalance Ib is the circulating current Ic.
At start-up, each controller is responsive to a start sync command to implement a start-up procedure to generate the command Vx_n to ramp voltage Vc_n, hence the regulated voltage Vreg_n up from an initial start value (e.g. 0 Volts) to an initial value for the setpoint voltage Vsetpoint_n while commanding Zeff_n to move from the high value to the low value over a start-up period. Preferably the N power converters receive a common start sync command to synchronize the ramping up of Vc_n. The “ramp” may be linear, a sequence of steps or a higher order function. The transition of Zeff_n may be a step, sequence of steps, piece-wise linear or a linear or higher order function. Because start-up is controlled, the transition may be tied to time over the start-up period as a proxy for the value of Iout_n. Alternately, the controller could execute the transitions as a function of Isense_n as indicative of Iout_n.
At steady-state, command Vx_n is generated to control Vc_n to control regulation of Vout while commanding Zeff_n in response to Isense to move between the high and lows values as Isense changes such that Zeff_n decreases as Iout_n increases to force sharing and reduce current imbalance at low levels of load current and improve regulation at higher levels of load current. The transition of Zeff_n may be a step, sequence of steps, piece-wise linear or a linear or higher order function.
In an embodiment, the multi slope output impedance controller is configurable to implement both the start-up and steady-state procedures to reduce the current imbalance and maintain load regulation.
In an embodiment, the multi slope output impedance controller is configurable via a mode input to implement control either for a masterless configuration of N parallel-connected power converters to reduce current imbalance during start-up and steady-state or for a single power converter to optimize load regulation over the range of supported load currents.
These and other features and advantages of the invention will be apparent to those skilled in the art from the following detailed description of preferred embodiments, taken together with the accompanying drawings, in which:
The present invention provides a multi slope output impedance controller capable of varying the effective impedance Zeff of a power converter to reduce a current imbalance between power supplies in a masterless configuration of N parallel-connected power supplies while maintaining load regulation during start-up and steady-state operation. Generally speaking, the controller commands a high value of Zeff_n when Iout_n is low to facilitate current sharing and reduce current imbalance Ib and commands a low value of Zeff_n when Iout_n is high to improve load regulation.
Referring now to
Each power converter 608 is depicted as a dependent source 614 in which a command voltage Vx_n is multiplied by a gain by a gain α_n to produce a controllable voltage Vc_n and is characterized by an open-loop output impedance Z_OL. The existence of energy source Vin is presumed in a dependent source. Voltage Vc_n is applied across an effective output impedance Zeff_n to supply an output current Iout_n at an output that is coupled through an external output impedance Z_ext_n to the load terminal 604. The total output impedance Zout_n=Zeff_n+Zext_n
Negative feedback controller 610 is configured to provide a negative feedback loop in which a regulated voltage Vreg_n at the output is compared to a setpoint voltage Vsetpoint_n to control command Vx_n to maintain regulation of Vreg_n and an output voltage Vout at the load terminal for varying load currents IL. A bandwidth of the negative feedback loop that controls output voltage Vreg_n may vary with load current, Vin, Vout and switching frequency, which can be either modeled or measured. In general, the bandwidth may drop as the load current is reduced.
The multi slope output impedance controller 612 is configured to sense a current Isense_n indicative of Iout_n to control Vsetpoint_n such that Vreg_n is reduced as Iout_n is increased to facilitate load current sharing among the plurality of power supplies (e.g. the common droop share), command a high value of Z_eff_n when Iout_n is less than a specified value to reduce a current imbalance Ib between the power supplies and to command a low value of Z_eff_n when Iout_n is greater than the specified value to improve the regulation of the output voltage Vout. The “specified value” may be an actual threshold value of Iout_n or may be a proxy such as a time indicating progression in a controlled start-up. As will be discussed later, the controller may receive a mode input to configure the power controller for a parallel-connected configuration such as shown in
Referring now to
Controller 800 includes CGC 802 responsive to Isense_n, an input voltage sense, a switching frequency, and a voltage reference Vref_n to generate a current reference, a gain command, a filter command and a setpoint command. A current error amplifier 804 compares Isense_n to the current reference to generate an error signal 806. A programmable gain amplifier 808 is responsive to the gain command to command the high and low values of the Zeff_n and amplify the error signal. In general, a higher gain corresponds to a larger positive Zeff. A negative gain can be used to set a negative Zeff. A filter 810 is responsive to the filter command to filter the amplified error signal to limit a bandwidth of an output impedance control loop to be less than a bandwidth of the negative feedback loop that controls Vre to achieve the desired response and stability of the output impedance controller. In a preferred embodiment, the CGC generates the filter command such that the bandwidth of the output impedance control loop tracks the bandwidth of the negative feedback loop up and down so that the impedance bandwidth is as high as possible without interfering with the output voltage bandwidth to optimize performance. An amplifier 812 responsive to the filtered amplified error signal and the setpoint command generates an offset to the setpoint voltage Vsetpoint_n such that when Isense_n is greater than the current reference the setpoint voltage Vsetpoint_n is reduced. The controller may be implemented with analog functions, digital hardware, software or a combination thereof.
Referring now to
At initiation and until all of the output voltages of the power converters are adequately regulated, the difference 904 in output voltages Vc_1 and Vc_2 can be significant and lead to a severe current imbalance. In a synchronously rectified configuration this will cause a circulating current Ic 906 to flow between the power converters. Accordingly, the controller adjusts the programmable gain to a very high level to set the high value 900 for Zeff to drive Ic 906 to close to zero amps. As start-up progresses, Iout_n increases and exceeds a setpoint 908. This may be determined by monitoring Isense_n directly or via design of the controlled start-up procedure. Knowing the ramp function, Iout_n can be calculated with sufficient accuracy and reliability over the start-up period and the Iout_n setpoint mapped to a progression or specific time in the start-up procedure. Preferably the setpoint corresponds to a value of Iout_n>2*Ic under no load conditions. Once this condition is satisfied, Zeff can be switched low without concern of inducing the circulating current Ic.
In this particular example, Zeff_n does not switch directly from its high to low values but follows a transition 910 from the high to low values that spans setpoint 908. The transition between the high and low values of Zeff_n can be a single step, a sequence of steps, a linear transition or a linear or higher order function depending upon the particular implementation. When start-up is complete, each power converter will supply a nominal Iout_n value, for example, sufficient to supply load current at the middle of its range to enter steady-state. The output voltages of each of the converters are fairly well regulated and the current levels are within the supported range. At this point, the controller adjusts the programmable gain to a low level, and perhaps a negative value, to set the low value 902 for Zeff to improve, or optimize, load regulation during steady-state operations. A negative Zeff_n would partially offset the positive value of Zeff_n producing a smaller positive output impedance Zout_n still sufficient to facilitate sharing of the load current with optimum load regulation.
In the case of passively rectified power converters, the same procedure of setting Zeff_n to a high value at the onset of start-up and switching to a low value at the completion of start-up is followed. The desirable effect of having a high value of Zeff_n at the onset is to implement droop share at low levels of Iout_n so that the power converters start to share load current much earlier in the start-up procedure, which improves the overall reliability and efficiency of the power supply. A low value of Zeff_n at the completion of start-up improves load regulation for steady-state operation.
Referring now to
The multi slope output impedance controller achieves better overall performance than the single slope output impedance controller, which must pick a fixed Zeff to support both start-up and steady-state operation of the power converters. The multi slope output impedance controller commands a high value of Zeff, higher than the fixed Zeff of the prior art, at low levels of Iout, which has the desirable effect of reducing the current imbalance between the power supplies. In the case of passively rectified converters, this has the desirable effect of forcing the converters to share the load current at lower levels during both start-up and steady-state. In the case of synchronously rectified converters, this has the desirable effect of essentially eliminating circulating current during both start-up and steady-state. In all cases, in the normal operating range of load currents at steady-steady state, the controller commands a low value of Zeff, lower than the fixed Zeff of the prior art, which improves the load regulation. The controller may even drive Zeff negative to optimize load regulation.
Referring back to
While several illustrative embodiments of the invention have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. Such variations and alternate embodiments are contemplated, and can be made without departing from the spirit and scope of the invention as defined in the appended claims.
Perry, Marty, Schaller, Robert J.
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